U.S. patent number 10,211,797 [Application Number 15/646,991] was granted by the patent office on 2019-02-19 for bidirectional amplifier.
This patent grant is currently assigned to TELEDYNE SCIENTIFIC & IMAGING, LLC. The grantee listed for this patent is Teledyne Scientific & Imaging, LLC. Invention is credited to Jonathan Roderick.
![](/patent/grant/10211797/US10211797-20190219-D00000.png)
![](/patent/grant/10211797/US10211797-20190219-D00001.png)
![](/patent/grant/10211797/US10211797-20190219-D00002.png)
![](/patent/grant/10211797/US10211797-20190219-D00003.png)
United States Patent |
10,211,797 |
Roderick |
February 19, 2019 |
Bidirectional amplifier
Abstract
A bidirectional amplifier includes first and second ports, with
a first summing node connected to the first port and a second
summing node connected to the second port. First and second gain
stages are connected between the first and second summing nodes,
respectively, and a first node. First and second feedback stages
are also connected between the first and second summing nodes,
respectively, and the first node. The amplifier operates in a first
mode in which an amplified version of a signal applied to the first
port is provided at the second port, or a second mode in which an
amplified version of a signal applied to the second port is
provided at the first port. The first and second gain stages are
preferably first and second common emitter cascode arrangements,
and the first and second feedback stages are preferably first and
second emitter followers.
Inventors: |
Roderick; Jonathan (Thousand
Oaks, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Teledyne Scientific & Imaging, LLC |
Thousand Oaks |
CA |
US |
|
|
Assignee: |
TELEDYNE SCIENTIFIC & IMAGING,
LLC (Thousand Oaks, CA)
|
Family
ID: |
60941416 |
Appl.
No.: |
15/646,991 |
Filed: |
July 11, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20180019719 A1 |
Jan 18, 2018 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
62361308 |
Jul 12, 2016 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H03G
1/0023 (20130101); H03F 3/62 (20130101); H03F
3/50 (20130101); H03F 1/22 (20130101); H03F
2200/69 (20130101); H03F 2200/75 (20130101) |
Current International
Class: |
H03F
1/22 (20060101); H03F 3/62 (20060101); H03G
1/00 (20060101) |
Field of
Search: |
;330/311 ;379/395 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Mottola; Steven J
Attorney, Agent or Firm: M. J. Ram and Associates
Parent Case Text
RELATED APPLICATIONS
This application claims the benefit of provisional patent
application No. 62/361,308 to Jonathan Roderick, filed Jul. 12,
2016.
Claims
I claim:
1. A bidirectional amplifier, comprising, first and second ports; a
first summing node connected to said first port; a second summing
node connected to said second port; a first gain stage connected
between said first summing node and a first node; a second gain
stage connected between said second summing node and said first
node; a first feedback stage connected between said first node and
said first summing node; a second feedback stage connected between
said first node and said second summing node; said bidirectional
amplifier arranged such that, in a first mode: said first port is
an input port and said second port is an output port; said first
summing node produces an output which varies with the difference
between a signal applied to said first port and the output of said
first feedback stage; said first gain stage provides an output
which varies with said first summing node output; said second
feedback stage receives the output of said first gain stage; and
said second summing node receives the output of said second
feedback stage and produces an output at said second port which
varies with said second feedback stage output; and in a second
mode: said second port is an input port and said first port is an
output port; said second summing node produces an output which
varies with the difference between a signal applied to said second
port and the output of said second feedback stage; said second gain
stage provides an output which varies with said second summing node
output; said first feedback stage receives the output of said
second gain stage; and said first summing node receives the output
of said first feedback stage and produces an output at said first
port which varies with said first feedback stage output.
2. The bidirectional amplifier of claim 1, wherein said first gain
stage comprises a first common emitter cascode arrangement and said
second gain stage comprises a second common emitter cascode
arrangement, and said first feedback stage comprises a first
emitter follower and said second feedback stage comprises a second
emitter follower, said bidirectional amplifier arranged such that,
in said first mode: said first gain stage is enabled; and said
first feedback stage provides feedback from the output of said
first gain stage to said first summing node and said second
feedback stage operates as an emitter follower stage; and in said
second mode: said second gain stage is enabled; and said second
feedback stage provides feedback from the output of said second
gain stage to said second summing node and said first feedback
stage operates as an emitter follower stage.
3. The bidirectional amplifier of claim 2, wherein in said first
mode, said second gain stage is disabled or adjusted in-situ or
during steady-state operation to meet system requirements, and in
said second mode, said first stage is disabled or adjusted in-situ
or during steady-state operation to meet system requirements.
4. The bidirectional amplifier of claim 3, wherein adjusting said
first or second gain stage comprises varying its magnitude and/or
phase.
5. The bidirectional amplifier of claim 1, wherein said first and
second gain stages have associated gain transfer functions A1(s)
and A2(s), respectively, and said first and second feedback stages
have associated feedback transfer functions f1,2(s) and f2,1(s),
respectively, wherein A1(s) and A2(s) can be identical or
different, and f1,2(s) and f2,1(s) can be symmetric or
asymmetric.
6. The bidirectional amplifier of claim 1, wherein said amplifier
is single-ended or differential.
7. A bidirectional amplifier, comprising, first and second ports; a
first circuit connected between said first port and a first node; a
second circuit connected between said second port and said first
node, the components of said first circuit being substantially
identical to the components of said second circuit, said
bidirectional amplifier having a symmetrical architecture around
said first node; said first and second circuits arranged to: in a
first mode, amplify a signal applied at said first port and provide
said amplified signal at said second port; and to: in a second
mode, amplify a signal applied at said second port and provide said
amplified signal at said first port; said bidirectional amplifier
having associated system gain, input impedance, and output
impedance characteristics, and circuitry arranged such that said
system gain, input impedance, and output impedance characteristics
can be designed independently of each other.
8. The bidirectional amplifier of claim 7, wherein said first and
second circuits comprise: first and second nodes coupled to said
first and second ports, respectively; first and second transistors
connected in a first common emitter cascode arrangement between
said first node and a third node; third and fourth transistors
connected in a second common emitter cascode arrangement between
said second node and said third node; a fifth transistor connected
between said third node and said first node; and a sixth transistor
connected between said third node and said second node; said
bidirectional amplifier arranged such that: in said first mode,
said first common emitter cascode arrangement is enabled, said
sixth transistor operates as an emitter follower and forms a gain
stage with said first common emitter cascode arrangement and said
fifth transistor operates as a feedback emitter follower, such that
said bidirectional amplifier amplifies a signal applied to said
first port and provides said amplified signal at said second port;
and such that: in said second mode, said second common emitter
cascode arrangement is enabled, said fifth transistor operates as
an emitter follower and forms a gain stage with said second common
emitter cascode arrangement and said sixth transistor operates as a
feedback emitter follower, such that said bidirectional amplifier
amplifies a signal applied to said second port and provides said
amplified signal at said first port.
9. The bidirectional amplifier of claim 8, wherein in said first
mode, said second common emitter cascode arrangement is disabled or
adjusted in-situ or during steady-state operation to meet system
requirements, and in said second mode, said first common emitter
cascode arrangement is disabled or adjusted in-situ or during
steady-state operation to meet system requirements.
10. The bidirectional amplifier of claim 9, wherein adjusting said
first or second common emitter cascode arrangement comprises
varying its magnitude and/or phase.
11. The bidirectional amplifier of claim 8, further comprising
first and second bias points coupled to said first and second
common emitter cascode arrangements, respectively, said first and
second bias points arranged to enable, disable, or adjust said
first and second common emitter cascode arrangements according to
system requirements.
12. The bidirectional amplifier of claim 8, further comprising a
load resistor connected between said third node and a supply
voltage.
13. The bidirectional amplifier of claim 8, further comprising; a
first resistor connected between said fifth transistor and said
first node; and a second resistor connected between said sixth
transistor and said second node.
14. The bidirectional amplifier of claim 8, further comprising: a
first current source which conducts a current Ibias1 connected
between said first node and a circuit common point; and a second
current source which conducts a current Ibias2 connected between
said second node and said circuit common point.
15. The bidirectional amplifier of claim 14, wherein
Ibias1=Ibias2.
16. The bidirectional amplifier of claim 14, wherein
Ibias1.noteq.Ibias2.
17. The bidirectional amplifier of claim 16, wherein in said first
mode, Ibias1=x and Ibias2=y, and in said second mode, Ibias1=y and
Ibias2=x.
18. The bidirectional amplifier of claim 14, wherein said first and
second current sources are digital-to-analog converters (DAC).
19. The bidirectional amplifier of claim 11, wherein said first and
second bias points are set to respective voltages with one or more
digital-to-analog converters.
20. The bidirectional amplifier of claim 11, wherein said first and
second bias points are set to respective voltages with first and
second switches, respectively, said first switch arranged to
connect the input to said first common emitter cascode arrangement
to either a circuit common point or to a first bias voltage, said
first common emitter cascode arrangement enabled when said first
switch connects the input to said first common emitter cascode
arrangement to said bias voltage, and said first common emitter
cascode arrangement disabled when said first switch connects the
input to said first common emitter cascode arrangement to said
circuit common point; said second switch arranged to connect the
input to said second common emitter cascode arrangement to either a
circuit common point or to a second bias voltage, said second
common emitter cascode arrangement enabled when said second switch
connects the input to said second common emitter cascode
arrangement to said bias voltage, and said second common emitter
cascode arrangement disabled when said second switch connects the
input to said second common emitter cascode arrangement to said
circuit common point; such that: when said bidirectional amplifier
is in said first mode, said first switch connects the input to said
first common emitter cascode arrangement to said first bias voltage
and said second switch connects the input to said second common
emitter cascode arrangement to said circuit common point, and when
said bidirectional amplifier is in said second mode, said first
switch connects the input to said first common emitter cascode
arrangement to said circuit common point and said second switch
connects the input to said second common emitter cascode
arrangement to said second bias voltage.
21. The bidirectional amplifier of claim 8, further comprising
first and second ac-coupling capacitors connected between said
first and second nodes and said first common emitter cascode
arrangement and said second common emitter cascode arrangement,
respectively.
22. The bidirectional amplifier of claim 8, further comprising
impedance matching circuitry connected between said first and
second ports and said first and second nodes, respectively.
23. The bidirectional amplifier of claim 8, wherein said first
transistor's base is coupled to said first node and its emitter is
connected to a circuit common point, and said second transistor's
base is coupled to a first bias voltage and its collector is
connected to said third node, the emitter of said second transistor
connected to the collector of said first transistor, and wherein
said third transistor's base is coupled to said second node and its
emitter is connected to said circuit common point, and said fourth
transistor's base is coupled to a second bias voltage and its
collector is connected to said third node, the emitter of said
fourth transistor connected to the collector of said third
transistor.
24. The bidirectional amplifier of claim 23, further comprising:
first and second resistors connected between the bases of said
second and fourth transistors and said first and second bias
voltages, respectively, and first and second capacitors connected
between the bases of said second and fourth transistors and said
circuit common point, respectively.
25. A bidirectional amplifier, comprising: first and second ports;
first and second nodes coupled to said first and second ports,
respectively; first and second ac-coupling capacitors connected
between said first and second nodes and third and fourth nodes,
respectively; first and second transistors connected in a first
common emitter cascode arrangement between said third node and a
fifth node; third and fourth transistors connected in a second
common emitter cascode arrangement between said fourth node and
said fifth node; a fifth transistor connected between said fifth
node and said first node; a sixth transistor connected between said
fifth node and said second node; a first current source which
conducts a current Ibias1 connected between said first node and a
circuit common point; a second current source which conducts a
current Ibias2 connected between said second node and said circuit
common point; and first and second bias points coupled to said
third and fourth nodes, respectively; said bidirectional amplifier
arranged such that: in said first mode, said first and second bias
points are arranged to enable said first common emitter cascode
arrangement and disable said second common emitter cascode
arrangement, said sixth transistor operates as an emitter follower
and forms a gain stage with said first common emitter cascode
arrangement and said fifth transistor operates as a feedback
emitter follower, such that said bidirectional amplifier amplifies
a signal applied to said first port and provides said amplified
signal at said second port; and such that: in said second mode,
said first and second bias points are arranged to enable said
second common emitter cascode arrangement and disable said first
common emitter cascode arrangement, said fifth transistor operates
as an emitter follower and forms a gain stage with said second
common emitter cascode arrangement and said sixth transistor
operates as a feedback emitter follower, such that said
bidirectional amplifier amplifies a signal applied to said second
port and provides said amplified signal at said first port.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates generally to amplifiers, and more
particularly to circuits capable of providing amplification
bidirectionally.
Description of the Related Art
There are a number of applications in which bilateral signal
amplification is desirable or necessary. For example, communication
and radar systems commonly use both transmit and receive
architectures to provide this functionality.
One way to provide bidirectional amplification is with the use of
two opposing amplifiers; this is illustrated in FIG. 1. Here, a
first amplifier A1 provides amplification between a first port PORT
1 and a second port PORT 2, and a second amplifier A2 provides
amplification between PORT 2 and PORT 1. In operation, either A1 or
A2 is powered on or enabled, depending on the desired amplification
direction.
Another approach is shown in FIG. 2. Here, rather than require that
the two opposing amplifiers be powered on or enabled, the direction
of amplification is determined by two SPDT switches S1 and S2. When
S1 and S2 are connected in the `up` position as shown in FIG. 2,
amplifier A1 provides amplification between PORT 1 and PORT 2;
similarly, when S1 and S2 are in the `down` position, amplifier A2
provides amplification between PORT 2 and PORT 1.
However, the two-opposing-amplifier approach shown in FIGS. 1 and 2
significantly increase system integration complexity, design layout
footprint, and cost due to parts count. In addition, mismatch
between the two amplifiers and the two switches (if used) is
inevitable, as are switch-related losses; these inherent flaws
diminish achievable system performance and are likely to result in
signal processing error.
SUMMARY OF THE INVENTION
A bidirectional amplifier is presented which overcomes some of the
problems discussed above, without increasing the design layout
footprint. The architecture allows real-time in situ swapping of
the input and output, and makes possible the reuse of common
components in, for example, communication systems that perform both
transmit and receive functions.
The present amplifier comprises first and second ports, with a
first summing node connected to the first port and a second summing
node connected to the second port. A first gain stage is connected
between the first summing node and a first node, and a second gain
stage is connected between the second summing node and the first
node. A first feedback stage is connected between the first node
and the first summing node, and a second feedback stage is
connected between the first node and the second summing node. The
bidirectional amplifier is arranged to operate in either a first
mode in which an amplified version of a signal applied to the first
port is provided at the second port, or a second mode in which an
amplified version of a signal applied to the second port is
provided at the first port.
Specifically, in the first mode: the first port is an input port
and the second port is an output port; the first summing node
produces an output which varies with the difference between a
signal applied to the first port and the output of the first
feedback stage; the first gain stage provides an output which
varies with the first summing node output; the second feedback
stage receives the output of the first gain stage; and the second
summing node receives the output of the second feedback stage (here
operating as a follower stage) and produces an output at the second
port which varies with the second feedback stage output.
And in the second mode: the second port is an input port and the
first port is an output port; the second summing node produces an
output which varies with the difference between a signal applied to
the second port and the output of the second feedback stage; the
second gain stage provides an output which varies with the second
summing node output; the first feedback stage receives the output
of the second gain stage; and the first summing node receives the
output of the first feedback stage (here operating as a follower
stage) and produces an output at the first port which varies with
the first feedback stage output.
The first and second gain stages preferably comprise first and
second common emitter cascode arrangements, respectively, and the
first and second feedback stages preferably comprise first and
second emitter followers, respectively. In the first mode, the
first gain stage is enabled and the second gain stage is adjusted
according to system requirements or disabled, the first feedback
stage provides feedback from the output of the first gain stage to
the first summing node, and the second feedback stage operates as
an emitter follower stage. In the second mode, the second gain
stage is enabled and the first gain stage is adjusted according to
system requirements or disabled, the second feedback stage provides
feedback from the output of the second gain stage to the second
summing node, and the first feedback stage operates as an emitter
follower stage.
These and other features, aspects, and advantages of the present
invention will become better understood with reference to the
following drawings, description, and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic of a known bidirectional amplifier.
FIG. 2 is a schematic of a known bidirectional amplifier.
FIG. 3 illustrates the general concept for a bidirectional
amplifier in accordance with the present invention.
FIG. 4 is a block diagram of one possible embodiment of a
bidirectional amplifier in accordance with the present
invention.
FIGS. 5a and 5b are block diagrams which illustrate the operation
of the bidirectional amplifier of FIG. 4 when amplifying from PORT
1 to PORT 2, and from PORT 2 to PORT 1, respectively.
FIG. 6 is a schematic diagram of one possible implementation of a
bidirectional amplifier in accordance with the present
invention.
FIG. 7 is a more detailed schematic diagram of one possible
implementation of a bidirectional amplifier in accordance with the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
The general concept for a bidirectional amplifier in accordance
with the present invention is shown in FIG. 3. The bidirectional
amplifier 10 comprises a first port 12 and a second port 14. The
bidirectional amplifier operates in two modes. In a first mode,
port 12 is an input port and port 14 is an output port, with the
signal provided by the amplifier to output port 14 being
proportional to a signal provided to the amplifier at input port
12. Similarly, in a second mode, port 14 is an input port and port
12 is an output port, with the signal provided by the amplifier to
output port 12 being proportional to a signal provided to the
amplifier at input port 14. A means of switching the bidirectional
amplifier between first and second modes would preferably be
provided.
A block diagram of one possible embodiment of the present
bidirectional amplifier is shown in FIG. 4. As above, the
bidirectional amplifier 10 includes a first port 12 and a second
port 14. A first summing node 16 is connected to first port 12, and
a second summing node 18 is connected to second port 14. A first
gain stage 20 is connected between first summing node 16 and a
first node 22, and a second gain stage 24 is connected between
second summing node 18 and first node 22. A first feedback stage 26
is connected between first node 22 and first summing node 16, and a
second feedback stage 28 connected between the first node and
second summing node 18.
The `first mode` operation of bidirectional amplifier 10 is
illustrated in FIG. 5a, as follows:
first port 12 is an input port and second port 14 is an output
port;
first summing node 16 produces an output which varies with the
difference between a signal applied to first port 12 and the output
of first feedback stage 26;
first gain stage 20 provides an output which varies with the output
of first summing node 16;
second feedback stage 28 receives the output of first gain stage
20; and
second summing node 18 receives the output of second feedback stage
28 and produces an output at second port 14 which varies with the
output of the second feedback stage, thereby providing
amplification from left-to-right. Here, second feedback stage 28
operates as a follower stage, and second gain stage 24 is adjusted
according to system requirements or is disabled. The magnitude
and/or phase of gain stages 20 and 24 may be varied in-situ or
during steady-state operation to meet the requirements of
application specific systems.
The `second mode` operation of bidirectional amplifier 10 is
illustrated in FIG. 5b, as follows:
second port 14 is an input port and first port 12 is an output
port;
second summing node 18 produces an output which varies with the
difference between a signal applied to second port 14 and the
output of second feedback stage 28;
second gain stage 24 provides an output which varies with the
output of second summing node 18;
first feedback stage 26 receives the output of second gain stage
24; and
first summing node 16 receives the output of first feedback stage
26 and produces an output at first port 12 which varies with the
output of the first feedback stage, thereby providing amplification
from right-to-left. Here, first feedback stage 26 operates as a
follower stage, and first gain stage 20 is adjusted according to
system requirements or is disabled. The magnitude and/or phase of
gain stages 20 and 24 may be varied in-situ or during steady-state
operation to meet the requirements of system application specific
systems.
First and second gain stages 20 and 24 have associated gain
transfer functions A1(s) and A2(s), respectively, and first and
second feedback stages 26 and 28 have associated feedback transfer
functions f1,2(s) and f2,1(s), respectively. A1(s) and A2(s) can be
identical or different. For example, both functions can be
narrowband, both wideband, one narrowband and the other wideband,
etc. Feedback stage functions f1,2(s) and f2,1(s) can be identical
or different, symmetric or asymmetric, etc., and can be implemented
with specific functions to provide desired effects. For example,
gain-peaking zeroes can be placed in the feedback stage functions,
to obtain an overall flatter gain response over frequency for the
amplifier. These functions can impact various amplifier
characteristics, such as the overall amplifier gain, as well as the
port impedances. A bidirectional amplifier as described herein can
be implemented using nearly any circuit technology, including
solid-state circuitry such as BJTs, HBTs, or CMOS FETs, vacuum
tubes, etc.
With respect to FIGS. 4, 5a, and 5b, the term "feedback" is
intended to encompass both feedback and follower functions. For
example, in the "first mode", first feedback stage 26 provides a
feedback function and second feedback stage 28 provides a follower
function, while in the "second mode", the first feedback stage
provides a follower function and the second feedback stage provides
a feedback function.
In practice, the present bidirectional amplifier has circuitry
connected between first and second ports which is arranged to, in a
first mode, amplify a signal applied at the first port and provide
the amplified signal at the second port, and in a second mode,
amplify a signal applied at the second port and provide the
amplified signal at the first port. An exemplary, basic
implementation of a bidirectional amplifier 30 per the present
invention is shown in FIG. 6. The amplifier's circuitry comprises
first and second ports 32 and 34, coupled to first and second nodes
36 and 38, respectively. First and second transistors Q1 and Q2 are
connected in a first common emitter cascode arrangement 40 between
first node 36 and a third node 42, and third and fourth transistors
Q3 and Q4 are connected in a second common emitter cascode
arrangement 44 between second node 38 and third node 42. A fifth
transistor Q5 is connected between third node 42 and first node 36,
and a sixth transistor Q6 is connected between third node 42 and
second node 38. An AC load resistor (R.sub.L) would typically be
connected between third node 42 and the supply voltage.
As noted above, the bidirectional amplifier 30 operates in first
and second modes. In the first mode, first common emitter cascode
arrangement 40 is enabled and second common emitter cascode
arrangement 44 is adjusted according to system requirements (as
discussed above) or disabled. Sixth transistor Q6 operates as an
emitter follower and forms a gain stage with first common emitter
cascode arrangement 40, and fifth transistor Q5 operates as a
feedback emitter follower, such that bidirectional amplifier 30
amplifies a signal applied to first port 32 and provides the
amplified signal at second port 34. As shown, the bases of Q2 and
Q4 are tied to DC bias points, which are AC grounds (zero impedance
at the frequency of interest). A finite impedance maybe introduced
at the base of Q2 and/or Q4 to produce a desired transfer
function.
In the second mode, second common emitter cascode arrangement 44 is
enabled and first common emitter cascode arrangement 40 is adjusted
according to system requirements or is disabled. Fifth transistor
Q5 operates as an emitter follower and forms a gain stage with
second common emitter cascode arrangement 44, and sixth transistor
Q6 operates as a feedback emitter follower, such that bidirectional
amplifier 30 amplifies a signal applied to second port 34 and
provides the amplified signal at first port 32. As above, the bases
of Q2 and Q4 are tied to DC bias points/AC grounds. A finite
impedance maybe introduced at the base of Q2 and/or Q4 to produce a
desired transfer function.
The present bidirectional amplifier may be realized with only a few
components more than that needed to implement a single amplifier.
This improves system loss and drastically lowers the required
layout real estate compared to an implementation which uses two
amplifiers. Also, utilizing a single amplifier as described herein
reduces undesired mismatch inherent with a two amplifier solution.
The novel bidirectional amplifier is a preferably a single,
symmetrical architecture, which eliminates losses associated with
switches, signal processing error resulting from component
mismatch, and additional overhead--all of which might be incurred
with a two amplifier approach.
As noted above, the present novel circuit topology allows for
bidirectional amplification without significantly increasing the
design layout footprint required for a unidirectional amplifier.
The architecture allows real-time in situ swapping of the input and
output. This allows for the reuse of common components and key
system resources in, for example, communication systems that
perform both transmit and receive functions. The bidirectional
amplifier described herein is useful with any application that
requires electrical signals that need to move in a bidirectional
manner. Beamforming radar and fiber optic communications are
exemplary applications.
A detailed implementation of a preferred embodiment of the present
bidirectional amplifier is shown in FIG. 7. As in FIG. 6, the
bidirectional amplifier 48 comprises first and second nodes 50, 52
coupled to first and second ports 54, 56, respectively, first and
second transistors Q7, Q8 connected in a first common emitter
cascode arrangement 58 between first node 50 and a third node 60,
third and fourth transistors Q9, Q10 connected in a second common
emitter cascode arrangement 62 between second node 52 and third
node 60, a fifth transistor Q11 connected between third node 60 and
first node 50, and a sixth transistor Q12 connected between third
node 60 and second node 52.
There are numerous ways in which the amplifier can be toggled
between its first and second operating modes; one possibility is to
have first and second bias points coupled to the first and second
common emitter cascode arrangements, respectively, and arranged
such that they can selectively enable or disable the first and
second common emitter cascode arrangements. This is illustrated in
FIG. 7, in which a first bias point 64 is coupled to first common
emitter cascode arrangement 58, and a second bias point 66 is
coupled to second common emitter cascode arrangement 62. First and
second common emitter cascode arrangements 58 and 62 can be
enabled, disabled, or adjusted according to system requirements (as
discussed above) by controlling the voltages at bias points 64 and
66.
The bias point voltages can be established in any number of
different ways. For example, first and second bias points 64 and 66
can be set to respective voltages with one or more
digital-to-analog converters (DACs). Another possible method by
which the voltages at bias points 64 and 66 can be set is with
first and second switches, respectively; this method is illustrated
in FIG. 7. Here, a first switch 68 is arranged to connect the input
to first common emitter cascode arrangement 58 to either a circuit
common point or to a first bias voltage Vb1 (preferably via a
resistor R1), such that the first common emitter cascode
arrangement is enabled when switch 68 connects bias point 64 to
Vb1, and is disabled when switch 68 connects bias point 64 to a
circuit common point (such as ground). Similarly, a second switch
70 is arranged to connect the input to second common emitter
cascode arrangement 62 to either a circuit common point or to a
second bias voltage Vb2 (preferably via a resistor R2), such that
the second common emitter cascode arrangement is enabled when
switch 70 connects bias point 66 to Vb2, and is disabled when
switch 70 connects bias point 66 to a circuit common point (such as
ground).
In operation, switches 68 and 70 would be operated in complementary
fashion. In the amplifier's first mode, in which port 1 (54) is the
input and port 2 (56) is the output, switch 68 connects bias point
64 to Vb1 and switch 70 connects bias point 66 to circuit common,
thereby enabling first common emitter cascode arrangement 58 and
disabling second common emitter cascode arrangement 62. In the
amplifier's second mode, in which port 1 (54) is the output and
port 2 (56) is the input, switch 68 connects bias point 64 to
circuit common and switch 70 connects bias point 66 to Vb2, thereby
enabling second common emitter cascode arrangement 62 and disabling
first common emitter cascode arrangement 58. Note that Vb1 and Vb2
would typically be equal, though this is not essential. Bias
voltages Vb1 and Vb2 set the current density through the first
amplification stage (input), which in turn sets the open loop gain
of the first amplification section. The current density can also be
used to adjust other performance metrics of the amplifier, such as
unity gain frequency, etc. Just as with any amplifier, the device
bias in the gain stage may be used to adjust gain and frequency
response.
A bidirectional amplifier as shown in FIG. 7 preferably includes a
first current source 72 which conducts a bias current Ibias1
connected between first node 50 and a circuit common point, and a
second current source 74 which conducts a bias current Ibias2
connected between second node 52 and the circuit common point.
Ibias1 and Ibias2 may be equal or different. In one embodiment,
with the amplifier operating in its first mode, Ibias1 can be equal
to a value x and Ibias2 equal to a value y, and then when operating
in its second mode, Ibias1 becomes equal to y and Ibias2 becomes
equal to x. First and second current sources can be implemented in
any of a number of different ways; for example, respective DACs
could be used to provide Ibias1 and Ibias2. The exact values of
Ibias1 and Ibias2 can be chosen to adjust amplifier performance.
For instance, the amplifier gain, input and output impedance can
all be controlled by these bias currents.
A bidirectional amplifier as shown in FIG. 7 suitably includes a
resistor R3 connected between Q11 and first node 50, and a resistor
R4 connected between Q12 and second node 52. The impedances R3 and
R4 can be used in conjunction with Q11 and Q12 to dictate a
specific amplifier performance. While shown as purely real
impedances in FIG. 7, these impedances may be realized as complex
impedances to control amplifier gain, phase, or impedance.
Bidirectional amplifier 48 may also include first and second
ac-coupling capacitors C1 and C2, connected between first and
second nodes 50 and 52 and first common emitter cascode arrangement
58 and second common emitter cascode arrangement 62, respectively.
C1 enables Q7 and Q11 to be biased independently, and C2 has the
same effect for Q9 and Q12.
In addition to adjusting amplifier bias points and impedances,
impedance matching may be accomplished by using additional passive
components. These passive element circuits 80 and 82 may be
connected between first and second ports 54 and 56, respectively,
and the other amplifier circuitry. For example, impedance matching
circuitry 80 may comprise an inductor L1 and a capacitor C3, and
impedance matching circuitry 82 may comprise and inductor L2 and a
capacitor C4. These components may be unnecessary if the signals
being amplified are low frequency.
The bases of Q8 and Q10 may be connected directly to fixed
voltages, as shown in FIG. 6. Alternatively, as shown in FIG. 7,
the bases of Q8 and Q10 can be connected to fixed voltages Vb3 and
Vb4 via resistors R5 and R6, respectively, with capacitors C5 and
C6 connected between the bases of Q8 and Q10 and a circuit common
point. When properly selected, C5 and C6 allow there to be zero
impedance at Q8 and Q10, providing stability over frequency. A
shunt-peaking inductor L3 is shown connected in series with load
resistor R.sub.L, though this is not essential.
When operating in the first mode, amplification proceeds
left-to-right in FIG. 7. In this mode, an input signal provided to
Port 1 is coupled to first common emitter cascode arrangement 58
via AC coupling capacitor C1. First common emitter cascode
arrangement 58 couples the signal to node 60, with Q11 serving as a
feedback emitter follower. The signal at node 60 is coupled to node
52--and thus output Port 2--via emitter follower transistor
Q12.
When operating in the second mode, amplification proceeds
right-to-left in FIG. 7. In this mode, an input signal provided to
Port 2 is coupled to second common emitter cascode arrangement 62
via AC coupling capacitor C2. Second common emitter cascode
arrangement 62 couples the signal to node 60, with Q12 serving as a
feedback emitter follower. The signal at node 60 is coupled to node
50--and thus output Port 1--via emitter follower transistor
Q11.
When amplification is left-to-right, the current through Q11 sets
the amplifier's input impedance, which can be further tuned with
Ibias1; in this case, Ibias2 can be used to set the amplifier's
output impedance. The roles of Ibias1 and Ibias2 are reversed for
right-to-left amplification. It is the feedback loop formed with
Q11 (for left-to-right) or Q12 (for right-to-left) that makes the
bidirectional functionality possible.
Note that, though FIGS. 6 and 7 depict a single-ended amplifier,
the concepts described herein are fully applicable to a
differential amplifier configuration.
The embodiments of the invention described herein are exemplary and
numerous modifications, variations and rearrangements can be
readily envisioned to achieve substantially equivalent results, all
of which are intended to be embraced within the spirit and scope of
the invention as defined in the appended claims.
* * * * *